1. Field of the Invention
This invention relates to electrophotography and particularly to improved corona generating apparatus for applying an electrostatic charge onto a recipient surface.
2. Description of the Prior Art
In known electrophotographic reproduction apparatus such as copiers or duplicators, an electrostatic charge is deposited on an area of a photoconductor as the area is moved past a corona current generating station. The photoconductor is then moved to an exposure station where the area is exposed to image-forming radiation to form a latent electrostatic image of a document to be copied. The latent image is thereafter developed and in the case of plain-paper copiers and duplicators subsequently transferred to a paper, upon which the copied image is to appear. Thereafter, the photoconductor is cleaned and otherwise made ready for the next copy cycle.
In such apparatus, it is important to impart a generally uniform charge over the area upon which the latent image is to be formed. Too low a charge in portions of the area may result in weak, washed-out looking areas on copies, and too great a charge in portions of the area may result in areas on copies being too dark relative to other areas. Therefore, copy quality, particularly with pictorial subject matter, is affected seriously where a non-uniform charge is placed on the photoconductor.
In the apparatus referred to above, development of the latent image is effected with electrostatically charged powder-like particles known as toner that are brought into surface contact with the photoconductor and are held thereon electrostatically in a pattern corresponding to the latent electrostatic image. Because of the fine nature of the toner and rapid movement of the photoconductor, particles of toner tend to become entrained in air currents within the apparatus and are carried to unwanted areas of the apparatus including the corona generating station.
The deposition of toner particles on a coronode wire of a corona generating station has a deleterious effect on the charging efficiency and charging uniformity of the coronode. In U.S. Pat. No. 3,496,352, a self-cleaning corona generating apparatus is disclosed which includes a high voltage power supply that is connected to a coronode or corona current generating electrode for generating a corona current. Also connected to the coronode is a coil comprising the secondary of a second power supply which may be selectively enabled to heat the coronode to vaporize toner particles depositing on the wire. An undesirable feature of this solution is the requirement of multiple power supplies each needed to accomplish a specific function. The reduction in the number of parts comprising electrophotographic reproduction apparatus comprises a continuing objective of manufacturers in their attempt to make these apparatus smaller and less expensive. The invention is therefore directed to the problem of heating of a corona generating electrode employing fewer parts than known apparatus of the prior art.